The Survival Paradox of Close-In Planets Orbiting Red Clump Giants
Abstract
Close-in planets orbiting core-helium-burning red-clump (RC) giants directly challenge tidal-engulfment theory, which predicts that planets within about 1 au of Sun-like stars should be engulfed during red-giant-branch (RGB) expansion. The existence of such survivors would imply missing physical processes in the late stages of stellar and planetary evolution. Yet only one such "forbidden" planet had been identified to date. Here we report three systems-24 Boo b, HD 12648 b, and TYC 4282-605-1 b-whose host stars are confirmed red-clump giants through asteroseismology, showing that each has already undergone dramatic expansion and contraction following helium ignition. Their planets now reside at orbital separations smaller than the maximum stellar radii attained during the RGB phase, implying that they should not have survived. Among them, 24 Boo b orbits at only 0.183 au with a 30-day period, making it the closest planet known around a red-clump giant. These discoveries demonstrate that this paradox is not an isolated anomaly but signals the emergence of a new class of evolved planetary systems. Their survival defies current models of stellar-planetary coevolution and points to unexplored physics shaping planetary architectures around post-RGB stars.
Versions
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BibTeX
@misc{lin2026survival,
title = {{The Survival Paradox of Close-In Planets Orbiting Red Clump Giants}},
author = {Wen-Xu Lin and Sheng-Bang Qian and Qi-Bin Sun and Li-Ying Zhu and Wen-Ping Liao and Ting Li and Fu-Xing Li and Xiang-Dong Shi and Tao Wang and Ergang Zhao and Huiting Zhang and Ping Li},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.04544},
eprint = {2611.04544},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.04544},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The Survival Paradox of Close-In Planets Orbiting Red Clump Giants
AU - Wen-Xu Lin
AU - Sheng-Bang Qian
AU - Qi-Bin Sun
AU - Li-Ying Zhu
AU - Wen-Ping Liao
AU - Ting Li
AU - Fu-Xing Li
AU - Xiang-Dong Shi
AU - Tao Wang
AU - Ergang Zhao
AU - Huiting Zhang
AU - Ping Li
PY - 2026
DA - 2026/11/03
PB - arXiv
DO - 10.48550/arxiv.2611.04544
UR - https://arxiv.org/abs/2611.04544
AB - Close-in planets orbiting core-helium-burning red-clump (RC) giants directly challenge tidal-engulfment theory, which predicts that planets within about 1 au of Sun-like stars should be engulfed during red-giant-branch (RGB) expansion. The existence of such survivors would imply missing physical processes in the late stages of stellar and planetary evolution. Yet only one such "forbidden" planet had been identified to date. Here we report three systems-24 Boo b, HD 12648 b, and TYC 4282-605-1 b-whose host stars are confirmed red-clump giants through asteroseismology, showing that each has already undergone dramatic expansion and contraction following helium ignition. Their planets now reside at orbital separations smaller than the maximum stellar radii attained during the RGB phase, implying that they should not have survived. Among them, 24 Boo b orbits at only 0.183 au with a 30-day period, making it the closest planet known around a red-clump giant. These discoveries demonstrate that this paradox is not an isolated anomaly but signals the emergence of a new class of evolved planetary systems. Their survival defies current models of stellar-planetary coevolution and points to unexplored physics shaping planetary architectures around post-RGB stars.
ER -